Former teacher Kaing Guek Eav -- better known as Duch -- appeared before a UN-backed war crimes court set up to deal with senior members of the 1975-1979 communist movement which killed up to two million people.

Wearing a white striped shirt, the frail 66-year-old heard charges that prisoners at the notorious Tuol Sleng prison he ran were subjected to beatings, suffocation and electrocution before being killed.

"I have already been notified of the charges against me," Duch told the court in response to initial questions, after greeting judges in the traditional Cambodian manner of putting his hands together.

"Before I was arrested by the military court, I was a teacher."

Duch sat in the dock while a clerk read the order charging him with war crimes, crimes against humanity, premediated murder and torture relating to his time as head of Tuol Sleng, also known as S21.

He faces life in prison if found guilty.

"Several witnesses said Duch was feared by everyone at S21. He enforced both the general rules of the (Khmer Rouge) in relation to the security police, as well as strict rules which he devised for the operation of S21," the clerk said.

"In addition to executing prisoners condemned in advance as traitors, an overriding purpose of S21 was to extract confessions from prisoners in order to uncover further networks as possible traitors."

The clerk said Duch permitted his staff to use torture techniques including beatings, electrocutions, placing plastic bags over prisoners' heads or pouring water into their noses.

Prosecutors and defence lawyers will make their opening statements for the trial on Tuesday and Duch is expected to apologise in court later this week. The trial is expected to last several months.

"It's certain that he will use the opportunity given to him to speak to the judges, to the victims and, beyond that, with the Cambodian population," Duch's French lawyer Francois Roux told AFP.

But many of the hundreds of Khmer Rouge survivors who watched the hearing behind bulletproof glass in an auditorium appeared reluctant to forgive the past.

"I am angry because they killed my wife, and I am happy because I have the court to try Khmer Rouge leaders," said Bou Meng, one of the handful of people who survived Tuol Sleng because his artistic skills were useful to the regime.

Duch, who became a born-again Christian while in hiding in the 1990s, previously told investigators that the decision to arrest people and send them to Tuol Sleng was made by the Khmer Rouge central committee.

He also denies personally torturing or executing prisoners, although he has consistently accepted responsibility for the atrocities at Tuol Sleng.

Many Cambodians believe the controversial tribunal, established in 2006 after nearly a decade of negotiations between Cambodia and the United Nations, is the last chance to find justice for the Khmer Rouge's crimes.

The joint trial of four other leaders of the 1975-1979 regime is set to start later this year after Duch's trial is completed, although no date has yet been set.

Tuol Sleng was at the heart of the Khmer Rouge's security apparatus and thousands of inmates were taken from there during Duch's tenure for execution at nearby Choeung Ek, an orchard now known as the "Killing Fields."

Many were allegedly forced to confess that they were spies for the US Central Intelligence Agency, the Soviet KGB or for neighbouring Vietnam.

Led by Pol Pot, the Khmer Rouge wiped out nearly a quarter of the population through starvation, overwork and execution as they tried to take society back to a rural "Year Zero" in a tragic spin-off to the Vietnam War.

Pol Pot died in 1998.

Duch has been detained since 1999, when he was found working as a Christian aid worker in the jungle, and was formally arrested by the tribunal in July 2007. He was indicted last year.